Synergistic Photophysical and Mechanical Enhancement in Europium Supramolecular Hydrogel by Incorporating Gd(DPA)₃...

Lanthanide hydrogels HGLn with iminodiacetic acid (Ln = Eu and Gd) and Na₃[Ln(DPA)₃]·9H₂O complexes (DPA = dipicolininate) were successfully synthesized via hydrothermal microwave-assisted and via precipitation, respectively. Incorporation of Ln(DPA)₃ complexes into the HGLn hydrogels resulted in the improvement of the spectroscopic properties and mechanical behavior. Rheological studies of the europium hydrogels doped with Gd(DPA)₃ complex (HGEu-Gd) showed a significant increase in the stiffness of the material by increasing the concentration of the incorporated complex. This effect also influences the increase in luminescence intensity of the HGEu-Gd hybrid. A computational modeling study of the interaction between the complex and hydrogel matrix suggests that this interaction does not affect the coordination symmetry of either Eu³⁺ or Gd³⁺. On the other hand, there were changes in the corresponding emission lifetimes, although not accompanied by changes in the emission spectral profile. The individual contributions to the luminescence of the hybrid gel were related to the maintenance of individual material characteristics and those resulting from hydrogel-complex interactions.